FIG. 16 is a block diagram illustrating an exemplary configuration of a radio base station system. The radio base station system exemplified in FIG. 16 includes a radio network controller (RNC) 100, one or a plurality of radio equipment controllers (RECs) 200, and one or a plurality of pieces of radio equipment (REs) 300.
The REC 200 is connected to the RNC 100 in a mutually communicable manner by an interface called Iub. The REC 200 corresponds to a baseband processing unit which is one function (element) of a radio base station. Each RE 300 corresponds to a radio processing unit which is one function of the radio base station. In terms of effective use of an apparatus resource as the radio base station, the REs 300 can be installed separated from the baseband processing unit and as remote radio apparatuses that provide radio areas (cells or sectors) to remote locations, etc. At this time, the REs 300 are connected to the REC 200 in a mutually communicable manner using, for example, an electrical or optical serial interface (CPRI interface) called Common Public Radio Interface (CPRI).
For example, the REC 200 includes modulation and demodulation equipment (MDE) 201 and transmit/receive interfaces (TRX INFs) 202, and each RE 300 includes an amplifying unit 301, a transmit/receive unit (TRX) 302, and a transmit/receive antenna (ANT) 303. The transmit/receive interfaces 202 of the REC 200 are connected to the corresponding transmit/receive units 302 of the REs 300 by CPRI.
The MDE 201 modulates, by a predetermined modulation scheme, a downlink (DL) signal received from the RNC 100 and destined for a radio terminal present in a radio area (cell or sector) provided by an RE 300. The modulated signal is transferred to a transmit/receive interface 202 corresponding to the RE 300. Also, the MDE 201 demodulates, by a predetermined demodulation scheme, an uplink (UL) signal received from a transmit/receive interface 202 and transmits the demodulated signal to the RNC 100. Note that the DL and UL signals may include a control signal and user data.
The DL signal modulated by the MDE 201 is transmitted from the transmit/receive interface 202 to the transmit/receive unit 302 of the RE 300 over a CPRI link. In the RE 300, the transmit/receive unit 302 performs a predetermined radio transmission process, such as frequency conversion (up-conversion), on the signal received from the REC 200 and thereafter the amplifying unit 301 amplifies the signal to predetermined transmission power and then the signal is transmitted from the transmit/receive antenna 303 serving as a radio (Uu) interface.
On the other hand, a radio signal transmitted from a radio terminal present in a radio area provided by an RE 300 and received by the transmit/receive antenna 303 is subjected to low-noise amplification, etc., by the amplifying unit 301, and thereafter the signal is transmitted to the transmit/receive unit 302. Thereafter, the received radio signal is subjected to a predetermined radio reception process, such as frequency conversion (down-conversion), by the transmit/receive unit 302 and then the signal is transmitted to a corresponding transmit/receive interface 202 of the REC 200 by a protocol (CPRI link) on the CPRI interface. The signal received by the transmit/receive interface 202 of the REC 200 is transferred to the MDE 201 and demodulated by the MDE 201.
The above-described radio base station system can only allow an RE 300 to be directly connected to the REC 200 by a CPRI link.
(Patent Document 1) Published Japanese Translation of PCT Application No. 2007-511955
(Patent Document 2) Published Japanese Translation of PCT Application No. 2007-529926
(Patent Document 3) Japanese Patent Application Laid-Open No. 2007-306362
(Non-Patent Document 1) CPRI Specification V3.0 (Oct. 20, 2006), “Common Public Radio Interface (CPRI); Interface Specification”, [searched on Apr. 25, 2008], Internet <URL: http://www.cpri.info/downloads/CPRI_v—3—0—2006-10-20.pdf>